1. Field of the Invention
The present invention relates to a repelling force apparatus of a power steering system for a vehicle, and in particular to a repelling force apparatus of a power steering system for a vehicle which is capable of increasing a steering force for thereby generating a certain difference in an operation force of a steering handle based on a running speed of a vehicle.
2. Description of the Background Art
Generally, in a hydraulic pressure steeling system which generates a steering force using a hydraulic operator, an output shaft and steering handle which are connected with steering wheels are connected on the same axis. Therefore, in the case that a steering torque is applied to the steering handle, a certain relative variation occurs between an input shaft and an output shaft based on a torsion of a torsion bar, so that a certain oil is applied to an operation chamber corresponding to a direction of a steering torque by a rotary valve between an input shaft and a valve body based on the relative variation.
As shown in FIG. 1, an interrelationship between a steering torque applied to the steering handle and a steering sub-force generated by a hydraulic operator is determined based on a torsion characteristic of the torsion bar, so that as the variation is increased, the amount of the torque is increased. Therefore, since the variation of the hydraulic pressure with respect to the steering torque needs a large hydraulic pressure in the case that a vehicle is stopped and runs at a low speed, the characteristic of an interval xe2x80x9caxe2x80x9d is used, and in the case that the vehicle runs at an intermediate speed and high speed, since it is possible to steer using a small hydraulic pressure, the characteristic of an interval xe2x80x9cbxe2x80x9d in which a small hydraulic pressure is used is used.
However, when setting the value of the torque of the steering handle based on a stop or low speed running state with respect to the variation of the hydraulic pressure based on the variation of the torque, it is possible to steer using a very small torque in the case that the vehicle runs at a high speed, so that an instable state occurs in a straight drive. On the contrary, when setting the value of the torque of the steering handle to a large value based on an intermediate or high speed running state, it is impossible to obtain enough steering sub-force.
Therefore, in the case that the vehicle is stopped or runs at a low speed by changing the slope of a variation graph of a torque with respect to a torsion variation of a torsion bar and a hydraulic pressure with respect to the torque in accordance with a running speed of the vehicle, a steering sub-force is increased using a small torque of the steering handle. In the case that the vehicle runs at an intermediate speed or high speed, a repelling force apparatus capable of increasing a steering repelling force is used.
A repelling force apparatus using an electric magnetic force is widely used for the above-described repelling force apparatus. The repelling force apparatus which uses the electric magnetic force is disclosed in the U.S. Pat. No. 5,119,898. In the above U.S. Pat. No. 5,119,898, a capsule type exciting coil 130, a cylindrical permanent magnet ring 104 and a pair of cylindrical ferromagnetic members 106 and 108. The cylindrical permanent magnetic ring 104 is fixed to a hub of a rotor installed at an outer portion of a sleeve for a revolution with respect to a valve body. In addition, the cylindrical rotation ferromagnetic members 106 and 108 are fixed at an inner portion of a spool shaft for a rotation together with the spool shaft.
The cylindrical permanent magnetic ring 104 is extended in an axial direction, so that the magnetic poles are alternately formed in a radial direction. FIGS. 4A and 4B are views of a flow of a magnetic field of a rotary magnetic circuit in a conventional repelling force apparatus.
In a state that a steering operation force is not applied to a steering handle, the path of the magnetic flow is formed in a central alignment as shown in FIG. 4A. However, when a steering operation force is applied to the steering handle, the cylindrical permanent magnet ring 104 is rotated based on the rotation of the valve body, so that the center of the magnetic flow path is distorted as shown in FIG. 4B.
In the thusly distorted magnetic flow path, the cylindrical permanent magnet ring 104 has a characteristic to be moved to the original position by the central alignment recovering force. The above-described force is applied as a repelling force with respect to the steering sub-force. Therefore, it is possible to adjust the steering sub-force based on a magnetic field by adjusting an intensity of the central alignment recovering force generated by the capsule type exciting coil 130.
As shown in FIGS. 5A and 5B, the toothed portions 120 and 122 formed in the cylindrical rotational ferromagnetic members 106 and 108 are protruded in a rectangular shape and are opposite to each other. Therefore, in the operational force variation by the magnetic force, as shown in FIG. 6, a straight line increase is implemented compared to the basic characteristic of the torsion bar. Therefore, as shown in FIG. 7, as a certain torque is generated by rotating the steering handle, in the case that the characteristic of the valve does not have a non-sensitive portion in which the pressure of the value is generated, it is possible to obtain a variable characteristic of the pressure-to-torque.
However, as shown in FIG. 8, in the case that there is a non-sensitive portion in which there is not a variation in the pressure of the valve even when the torque is generated by rotating the steering handle, as shown in FIG. 9, the non-sensitive portion of the valve characteristic is increased by a linear increase of the torque based on the torque generated by the variation of the torsion bar which is varied in accordance with the rotational angle of the steering handle.
Accordingly, it is an object of the present invention to provide a repelling force apparatus of a power steering system for a vehicle which is capable of obtaining various type linear and/or non-linear characteristics in a state that the characteristic of a valve is varied based on a running speed of a vehicle.
To achieve the above object, there is provided a repelling force apparatus of a power steering system for a vehicle in which the teeth formed in a pair of the rotational ferromagnetic members are formed in a trapezoid shape, and the sizes of the opposite surfaces of the same are different in the repelling force apparatus of a power steering system for a vehicle having a plurality of teeth which are opposite each other based on 1:1 in a pair of rotational ferromagnetic members wherein there are provided an exciting coil, a permanent magnet and a pair of rotational ferromagnetic members.